It's beyond me why rails thinks it should dictate how to write/manage/package javascript.
As a newbie-ish javascript developer I am continually learning from great projects like requirejs, enderjs, nodejs, commonjs (AMD in general), backbonejs, etc.
How arrogant do rails programmers have to be to dip their hand into javascript best practices? Honest question, because the better I get at programming the more I feel like rails is less necessary.
Bottom line is Rails is, and always has been, and opinionated framework, which you choose to buy in to. And even in recent years they've been better about letting you opt out of certain parts of it.
The asset pipeline is not arrogance it's convenience. If you have a better system for those tasks then you shouldn't use the pipeline, but for a lot of people the asset pipeline saves time and results in a faster, better experience for their end users.
Bundling a default that doesn't play well with lots of the client-side innovations hurts rails more than helps.
The asset pipeline as it is currently designed is monolithic and an all or nothing approach.